Abstract:
Weedy rice commonly causes a considerable reduction of rice yield due to its competition for resources with the
cultivated rice. At present, weedy rice infestation is becoming a major threat in rice fields in Matara district. The
present study assessed the distribution and variation pattern of weedy rice in the district to make awareness on the
status of this weed menace to the farmers facilitating the possible management practices. In the first study, the weed
density (plants/m2) was measured using a quadrate from five different places of each of the 8 different locations, at a
minimum 5 m distance between two populations during south western monsoon, 2009. In the second study, seeds
collected from mature weedy rice panicles from six locations were transplanted at the research field in a Randomized
Complete Block Design. Data on 13 agro-morphological traits were collected and analyzed using Principal
Component Analysis (PCA) followed by Cluster analysis. Results showed that, highly infested weedy rice fields were
observed from Thihagoda (22-25 plants/m2) and the lowest (3-5 plants/m2) recorded from Kotapola, Pitabeddara
and Akuressa fields. The first two PCs explained over 90% of the total variation. The first Principal Component (PCI)
which accounted for 73% was positively related to both heights at the seedling stage and booting stage, seed length,
seed width and seed weight. PC2 accounted for 20% of the total variation was mainly related to number of total seeds
per plant. There is a wide variation in the distribution of weed within the district and a large diversity in the
accessions of weedy rice in different rice growing areas of Matara district.
